BMFS result from hematopoietic progenitor or stem cell failure within the bone marrow. Specific causes of this problem, however, have been difficult to identify, as BMFS occur sporadically. For the same reason, few studies have been conducted to find out more about these diseases and to develop more appropriate and effective therapies. Aplastic anemia (AA) is the most common of all BMFS. Other types of BMFS include the following: myelodysplastic syndrome (MDS); paroxysmal nocturnal hemoglobinuria (PNH); pure red cell aplasia (PRCA); amegakaryocytic thrombocytopenic purpura (ATP); and large granular lymphocyte leukemia (LGL leukemia). Though AA is the most common of the BMFS, all BMFS are closely related in terms of their symptoms and characteristics. This study will collect clinical and laboratory data from people with BMFS to identify the characteristics and biological markers specific to each disease as it evolves. This information will assist doctors and researchers to devise better therapies and diagnostic tests that will help improve the management of BMFS and cytopenias.